The invention concerns an x-ray diagnostic apparatus for making x-ray film photographs, with an automatic exposure timer which contains a radiation detector, a signal processing circuit for the output signal of the radiation detector, and a switch-off device for the x-ray tube, which receives a switch-off signal from the signal processing circuit when the x-ray film has been exposed to a predetermined radiation dose.
In an x-ray diagnostic apparatus of this type, it is possible for an exposure to proceed inadvertently up to a maximum time limit due to an operating error or circuit malfunction. Upon reaching this maximum time limit, the x-ray tube is switched off by means of an overload protection device. Faulty operation of this type can be due to a defective amplifier in the automatic exposure timer, for example. It is also possible, however, that the user has forgotten to dial the desired radiation measurement chamber of the radiation detector. Finally, it is also conceivable for the primary radiation diaphragm of the x-ray tube to be closed while the tube is switched on. In all these instances, the switch-off device of the automatic exposure timer does not receive any switch-off signal. The patient can thus be burdened with an undesirably high radiation dose. Moreover, the x-ray tube is loaded up to a very high limit.